Question

Let A and B he two sets then
(AUB)'U(A'UB)=A' how?​

Answer 1

Since AUB=A

It indicates B is a empty set or have same elements which set A have  because at union fuction also the answer is A.

So it it conclude that if set B is null set then

A∩B=A

and if set B have same element that set A have then

A∩B=A or A∩B=B.